The present invention relates to a method and to a system intended for analysis and measurement of liquid or gaseous constituents contained in a drilling fluid. The term constituents designates here hydrocarbons, for example C1 to C8, including benzene, toluene, xylene, or gases such as H2S, CO2, O2, H2, N2. These constituents are due to drilling operations carried out through formation layers, operations that have the effect of breaking the rock, thereby releasing the gases or the fluids contained in the rock pores. Drilling is conventionally carried out with a circulation of a fluid referred to as drilling fluid whose function, among others, is to clean the drill bit and to drive the rock debris up to the ground surface. The constituents in question are therefore also carried along to the surface by means of this carrier. It is clear that, considering the flow rate of the drilling fluid compared to the rate of destruction of the rock, the volume amount of said constituents is always relatively low compared to the volume of mud.
There are known installations allowing to carry out qualitative and quantitative measurements of the C1-C5 gas contained in a drilling fluid, measurements (or logging operations) allowing to identify the geologic zones drilled for borehole and/or staff safety reasons. Document FR-2,646,508 describes a process and a device for continuous sampling of gaseous samples contained in a solid-containing liquid, notably a drilling fluid. In this document, neither its degassing mode nor its transportation mode allows to extract and to transport the hydrocarbons possibly present in liquid form in the mud carried along to the ground surface.
The object of the present invention is to implement the conditions required for: extraction of gaseous or liquid constituents contained in a drilling fluid, transportation of these constituents in gaseous form, and analyses and measurements of these constituents. In order to carry out correct analyses, allowing to better determine the nature and the composition of the formations crossed by a borehole, the constituents must not condense in the elements of the system and the time of transit of these constituents between the point of extraction and the point of measurement must be acceptable to allow the drilling operation to be monitored.
The present invention thus relates to an extraction, analysis and measuring system intended for constituents carried along by a well fluid during drilling operations. The system comprises in combination:
draw-off means for taking a determined volume of the fluid,
extraction means for extracting, in vapour form, the constituents contained in the volume of fluid, comprising a space placed under underpressure,
a vapour transport line, a first end of which communicates with the space, the second end being connected to a vacuum pump,
sampling means placed in the vicinity of the second end, comprising a sampling loop that allows to sample a determined amount of the vapours circulating in said line,
distribution means that inject the amount into analysis and measuring means, and
means for controlling the temperature of the sampling means so as to prevent condensation of the amount of vapours.
The space that contains the drilling fluid drawn off can be sealed against the outer environment.
The space can comprise an inlet port for an auxiliary gas, air or nitrogen for example.
The extraction means can comprise means for heating said volume of fluid sampled.
The sampling loop can be mounted directly in parallel on the transport line.
The drilling fluid draw-off means can comprise a suction pump and/or a discharge pump.
The space can be at an absolute pressure ranging between 10 and 100 mb, and the suction of the vacuum pump can range between 1 and 10 mb.
The invention also relates to an extraction, analysis and measuring method intended for constituents carried along by a well fluid during drilling operations, wherein the following stages are carried out:
a volume of drilling fluid is drawn off and placed in a space belonging to extraction means intended for extraction of constituents in vapour form,
an underpressure is applied in the space by means of a line connecting the analysis and measuring means to the extraction means,
a determined amount of the vapours circulating in the line is drawn off in the vicinity of the analysis and measuring means,
the amount of vapours is injected into the analysis and measuring means,
the nature and/or the amount of the constituents vaporized in the extraction means is deduced.
According to the method, the underpressure and/or temperature conditions can be adjusted for extraction in vapour form as a function of the drilling parameters, for example the nature of the fluid, the flow rate, the ambient temperature, the time of transit in the line.
A feed flow rate of the auxiliary gas fed into the space can be adjusted.
An underpressure ranging between 10 and 100 mb in absolute pressure can be applied in the extraction space.